[ios] Fix TabGrid rotation bug for iPhoneX regarding SafeArea Management

CollectionViewControllers within a ScrollView do not have accurate safe area guides. So this CL manages the proper safe area insets manually through contentInset.
TableViews do manage it better, but only on sides in which they area attached to the scrollview. On sides that are not, it is not predictable.

- removes CollectionView use of safe area by setting UIScrollViewContentInsetAdjustmentNever.
- adds ScrollView safe area insets (which is always accurate) to contentInset to viewWillLayoutSubviews.
- maintains TableView safe area management defaults, but ensure that the leading safe area inset matches the scrollView's.

(iPhone7 iOS 10)https://drive.google.com/open?id=1RYMcO_ZthbAAv2qWtVJIqBlXKTNgJgub
(iPad iOS 11)https://drive.google.com/open?id=1ZX9kl4j8UHcluHwa6LHYXCyI2ANaKyJP

Bug: 860437

Change-Id: Ie622fb58c7a86c09d3bff23e73908b9f33bc659c
Reviewed-on: https://chromium-review.googlesource.com/1135945
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576569}
2 files changed